fix: Improve error handling in case of failure when retrieving API doc

[taban03]

Description

Propagate exception message to the UI in case of failure of retrieving API doc either from the service or from the cache. It covers the following cases:

1. The Swagger definition was retrieved but was not a valid JSON document. + message from the parser
2. The Swagger definition was retrieved but it was not a valid Swagger JSON document according to the schema + message from parser
3. The Swagger URL is not valid

Linked to #2315

Type of change

• fix: Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the style guidelines of this project
• PR title conforms to commit message guideline ## Commit Message Structure Guideline
• I have commented my code, particularly in hard-to-understand areas. In JS I did provide JSDoc
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• The java tests in the area I was working on leverage @nested annotations
• Any dependent changes have been merged and published in downstream modules

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
89.7% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud